This invention relates to a fluid displacement apparatus, and particularly to a fluid compressor or pump unit of the type which utilizes an orbiting fluid displacement member.
There are several types of fluid displacement apparatus which utilize an orbiting fluid displacement member driven by a Scotch yoke type shaft coupled to an end surface of the orbiting fluid displacement member. U.S. Pat. No. 1,906,142 to John Ekelof discloses a rotary fluid displacement apparatus provided with an annular, eccentrically movable piston or wall adapted to act within an annular cylinder with a fixed radial transverse wall. One end of the chamber defined by the movable piston and annular cylinder is the wall of the cylinder, and the other wall of the chamber consists of a cover disc connected to the annular piston. The annular piston is driven by a crank shaft. Other prior art fluid displacement apparatus are shown in U.S. Pat. Nos. 801,182 and 3,560,119.
Though the present invention applies to either type of fluid displacement apparatus; i.e., using either an annular-shaped fluid displacement wall or a scroll (spiroidal) shaped fluid displacement wall, the description or orbiting fluid displacement member will be limited to a scroll-type compressor. The term "orbiting fluid displacement member" is used to generally describe a movable fluid displacement member of any suitable configuration in fluid displacement apparatus; i.e., annular piston, scroll, etc.
U.S. Pat. No. 801,182 discloses a fluid displacement device including two scroll members each having an end plate and a spiroidal or involute spiral element. These scroll members are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between the spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scroll members shifts the line contacts along the spiral curved surfaces, and therefore, the fluid pockets change in volume. The volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion. Therefore, a scroll-type fluid displacement apparatus can be used to compress, expand or pump fluids.
Scroll-type fluid displacement apparatus can be used as refrigerant compressors in refrigerators or air conditioners. Such compressors need a driving power source; for example, the motor of an engine, to drive the compressor. The compressor generally expends the greatest driving power during start-up. Therefore, if the compressor is connected to the driving power source, the output of which is matched with the average power of the driving compressor, satisfactory power to start up the compressor would not be obtained.
One solution to avoid this disadvantage is to use a motor or engine with larger output power. However, the outer dimension or weight of the driving power source would increase so that the cost of the power source increases. Furthermore, the greatest electric current is expent to start up the motor or the starter for the engine.
Another construction used to avoid this disadvantage is a magnetic valve device which selectively connects the compressor's discharge line with its suction line. In this construction, the magnetic valve device opens a connecting passageway before the drive of the compressor stops so that discharge gas flows into the suction side through the passageway of the magnetic valve device. The next time the compressor is started, the compressor is driven through a stage or time period when the pressure in the suction and discharge chambers is balanced. Therefore, the temporary expenditure of a large amount of power during start-up of the compressor is prevented. However, this construction requires a control circuit to operate the magnetic valve device which has the disadvantage of being complicated and increasing the cost of the apparatus. Furthermore, if the sealing of the discharge valve of the compressor, which is provided with the magnetic valve device, deteriorates, the pressure of the suction and discharge chamber may balance at undesirable times because of flow back through the discharge valve.